SCPB- and FMRFamide-like immunoreactivities in lobster neurons: Colocalization of distinct peptides or colabeling of the same peptide(s)?

Virtually all of the SCP(B)-like immunoreactive neurons (ca. 60 cells) in the lobster Homarus americanus also contain FMRFamide-like immunoreactivity. Control experiments reveal that SCP(B)- and FMRFamide-like immunoreactivities are successfully preadsorbed with their specific antigens, while the normal staining pattern is retained following preadsorption of each antibody with the alternate peptide. These experiments potentially lead to the conclusion that the anti-SCP(B) and anti-FMRFamide antibodies are labeling distinct compounds that are colocalized in lobster neurons. The lobster nervous system does not, however, contain authentic FMRFamide, but rather several FMRFamide-like compounds (Trimmer et al., J. Comp. Neurol. 266:16-26, 1987). The most abundant of these is the octapeptide TNRNFLRFamide. Experiments demonstrate that SCP(B)-like immunoreactivity is completely preadsorbed with synthetic TNRNFLRFamide, while there is a significant or complete loss of staining after preadsorption of the FMRFamide antibody with this molecule. Met-enkephalin-Arg-Phe-amide (YGGFMRFamide), an extended opioid peptide containing the FMRFamide sequence, also preadsorbs SCP(B)- and FMRFamide-like immunoreactivities, while Met-enkephalin-Arg-Phe (YGGFMRF) has no effect on the staining properties of these antibodies. These results suggest that the SCP(B) antibody can bind to extended forms of FMRFamide-like molecules, and that anti-SCP(B) and anti-FMRFamide antibodies may be colabeling one or more FMRFamide-like molecules in lobster neurons.